LeDoux, Joseph E. “Emotions: How I’ve Looked for Them in the Brain."

Joseph E. LeDoux specializes in the use of animal models for studying emotion. In “Emotions: How I’ve Looked for Them in the Brain,” LeDoux describes his work on fear conditioning in rats. The rats are conditioned to associate a sound with a noxious stimulus. This sound then elicits the behavioral responses accompanying the emotional experience of fear: muscle tension, release of stress hormones, and so forth. Note that LeDoux distinguishes between the behavioral system and subjective feelings. It is the former, he argues, that should be seen as essential to understanding the function of emotions.

LeDoux uses a variety of techniques to relate fear behavior to specific circuits in the brain. First, lesion studies (selective damage to parts of the brain) and brain imaging techniques make it possible to locate the general regions involved. Next the circuits activated in fear responses can be followed by injecting tracer substances into those areas and recording the “firing patterns” of neurons in relation to various emotional states under a variety of learning paradigms. In this way, LeDoux has confirmed the crucial role of the amygdala, a distinctive cluster of neurons found deep in the anterior temporal lobe of each hemisphere. Inputs to the amygdala from sensory processes in the thalamus and cortex are key to processing fear stimuli, while projections from the amygdala to brainstem areas are involved in control of the behavioral, autonomic, and hormonal responses that constitute fear behavior. LeDoux notes that a variety of other brain systems are also involved in the various feeling states we term “emotions” in humans; only empirical research will show whether his work on fear generalizes to other emotions.

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